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Pregnancy, check of paternity - Online Doctor Chats

Date : 21-Feb-2012
User rating for this question
Good Posted in: Pregnancy
Answered by

General & Family Physician
Practicing since : 2008
Answered : 3388 Questions
User :   How accurate are first trimester ultrasounds for a conception date? I need to know which man is my unborn childs father. My due due is 2/27/2011 which was first given to me on July 8,2010 at an ultrasound daing me 6 and a half weeks. Had two more ultrasounds done: One on August 27, dating me 13 and 5 days with my due date still 2/27/2011 and another on October 11, dating me 20 weeks 1 day with my due date still 2/27/2011. If I had intercourse with guy A on May 23 and guy B on June 5, who is the father? Is two weeks difference enough time to be able to tell this? I also have had irregular periods and only have ultrasounds to go by, is the information given to me by an ultrasound accurate enough to determine paternity? THANK YOU!
Doctor :   Hi
User :   Hello
Doctor :  
Doctor :   let me read ur query
Doctor :   given ur history and details, it is not possible to know ur paternity by the given data
Doctor :   also the ultrasound is not specific for paternity analysis
Doctor :   Please let me know the LMP, so that i can help u accordingly
User :   I do not have an LMP date, I stopped taking birth control late April and my last period was May 2, the ultrasounds all done do not nearly match up to that, so my doctor has disregarded that
Doctor :   give me a few minutes
User :   thank you
Doctor :   the date of conception by calculating backwards is june 6th 2010
Doctor :   so guy B is the most probably the father of the child
User :   I wanted a second opinion from what my obgyn had told me. He told me that first trimester ultrasounds are very accurate, within 5 days. Since there are 14 days between the two instances I could rule out the first man, as sperm could survive a max of 5 days.
Doctor :   considering your LMP as may 2nd, the date of conception should be may 16th, and u had not had sex until may 23rd , guy A is unlikely the father at all
User :   my doctor said the LMP is void, as it was way off from the ultrasound reading
Doctor :   based on the EDD, calculating backwards, the DATE of conception is 6th june , which correspponds to the fater being the guy B
Doctor :   AS THE EDD is based on the USG , it is accurate that guy B is the father of the child to beborn
User :   can this be determined by the ultrasound?
Doctor :   the date of conception cannot be determined by the ultrasound
Doctor :   it is calculated by calculating backwards from the EDD
User :   how accurate is that?
Doctor :   98%
Doctor :   Women who have regular periods every 28 days have an easier time figuring out their conception dates, because they tend to ovulate around day 14 of their cycles.
Doctor :   Women with irregular periods do not always know when ovulation occurs, making it harder to pinpoint the exact date of conception
User :   so i can safely say that guy B is the father?
Doctor :   yes
User :   ok thank you
Doctor :   YOU are welcome
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